New procedure to Build Marble on windows

I added a new procedure to build on Windows using Visual Studio 2008.
I used VS2008 Professionnal on a x64 environment.
There is no complication in buildind 32 or 64bits versions, apart from obtaining a 64bit version of Qt.
It should be possible to use other versions of Visual Studio, including Express editions as no special Windows libraries are necessary, only Qt compiled for the matching environement